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 April 6, 2013, 09:07 PM #1 Cesure Senior Member   Join Date: March 2, 2013 Posts: 131 Poor Man's Chronograph Has anyone tried measuring bullet velocity with a PC soundcard? I found this PDF when I was searching for low budget chronographs. It details how to measure the time lapse between the sound of a gunshot and the sound of a target hit 50'-150' away. Then if you know the ballistic coefficient of the bullet you can calculate the MV. The theory sounds good, but I wonder if anyone has tested it against a chronograph.
 April 6, 2013, 10:13 PM #2 WWWJD Senior Member   Join Date: February 9, 2011 Location: Central KY Posts: 532 I don't know about poor man's... this assumes you have a laptop with a good sound card, a good mic and a pretty good sample rate. Then you'd have to be able to cursor accurately enough over your scope plot to get a good time measure. By the time you get to all that, you could have bought a crony! It'd be a fun experiment though. __________________ ~Mark NRA fo Life Member
 April 6, 2013, 10:43 PM #3 Onward Allusion Senior Member   Join Date: November 17, 2009 Location: IN Posts: 1,994 The F-1 is around \$80 new. A decent PC mic will run you \$30 and up. Assuming you already have a laptop, you will still need long enough range and steel targets. It would be an interesting exercise but I'd stick to the chrony. __________________ "You haven't lived until you've died." - various
 April 7, 2013, 01:39 AM #5 big al hunter Senior Member   Join Date: March 12, 2011 Location: Washington state Posts: 1,011 If you have to calculate the velocity anyway, you can set up a target at 100 and 200 yards. Zero at 100. Shoot at 200. Measure the drop and plug in the calculations until you have a velocity that matches your drop. Not as precise as a sound card, but less expensive. __________________ You can't fix stupid....however ignorance can be cured through education!
 April 7, 2013, 09:41 AM #6 Cesure Senior Member   Join Date: March 2, 2013 Posts: 131 Well, I've got the laptop and I've got the mic and the file explains how to compensate for the speed of sound and I found the freeware that the article mentions, so my investment so far is zero, but I guess the answer to my question is "No" so far. I might give it a try when the weather gets a little warmer, but I don't have a chrono, cheap or otherwise, to compare it to. At that price, I would be happy with +- 50'.
 April 7, 2013, 11:02 AM #7 Unclenick Staff   Join Date: March 4, 2005 Location: Ohio Posts: 12,125 The main problem will be ballistic coefficients. Bryan Litz measured quite a number for his book and found some manufacturers claimed BC's that turned out to be off 10% or more. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member
 April 7, 2013, 11:34 AM #8 Cesure Senior Member   Join Date: March 2, 2013 Posts: 131 The bullet velocity will only be averaged over the distance used to measure the peaks, so the velocity won't drop that much if the distance is minimized. and the BC won't be that important. For slower bullets, you can move the measuring distance in to decrease the interval, especially if you have low ambient noise and few nearby sources of echoes from the initial report. For faster bullets, you would need the 150' just to distinguish the target hit from the report, but still, you could probably assume that a 10% error in the BC isn't going to produce a huge error in the calculated MV. I guess it could depend on your definition of huge. I have slow and fast rounds to play with.
 April 8, 2013, 01:06 PM #9 Onward Allusion Senior Member   Join Date: November 17, 2009 Location: IN Posts: 1,994 If you have the time and inclination, I would be interested in hearing how the results compare under the two vastly different methods. Yeah, I'm a geek. __________________ "You haven't lived until you've died." - various
 April 8, 2013, 01:16 PM #10 eldermike Senior Member   Join Date: January 24, 2013 Location: NC Posts: 545 A typical sound card for recording is 96K or better. So if you have a really good sound card you can improve things. I have a firewire MOTU sound card that's 96K
April 8, 2013, 01:58 PM   #11
Cesure
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Join Date: March 2, 2013
Posts: 131
Quote:
 A typical sound card for recording is 96K or better. So if you have a really good sound card you can improve things. I have a firewire MOTU sound card that's 96K
96K what? I have a sound card that came integral to the laptop. I'll be trying that. It worked real well with just two handclaps using the Audacity freeware and the built in mic. I have a better mic to use for the testing. I'm not trying to get .1fps accuracy. I'll be happy with 50fps.

April 8, 2013, 02:43 PM   #12
pnolans
Member

Join Date: December 7, 2011
Posts: 95
Quote:
 Well, I've got the laptop and I've got the mic and the file explains how to compensate for the speed of sound and I found the freeware that the article mentions, so my investment so far is zero, but I guess the answer to my question is "No" so far. I might give it a try when the weather gets a little warmer, but I don't have a chrono, cheap or otherwise, to compare it to. At that price, I would be happy with +- 50'.
If you're a computer geek like me, as well as being a gun nut, the OP's idea is simply to make use of something we already have!
Which, if it turns out to be accurate, will be great. But then you'll need a chronograph to check it!
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April 8, 2013, 02:54 PM   #13
Cesure
Senior Member

Join Date: March 2, 2013
Posts: 131
Quote:
Thanks.

I've read about all these people who have chronies that are tempermental, provide suspect readings or end up getting shot, so I just wanted to avoid the downsides of owning one.

 April 8, 2013, 08:43 PM #14 eldermike Senior Member   Join Date: January 24, 2013 Location: NC Posts: 545 96K means sampling rate in Khz. The higher the rate the more accurate your method will be.
 April 8, 2013, 08:57 PM #15 Cesure Senior Member   Join Date: March 2, 2013 Posts: 131 I figured it might be Hz. I'm glad it wasn't 96K\$, That would kinda blow the whole poor man's theme.
 April 8, 2013, 10:14 PM #16 BumbleBug Senior Member   Join Date: March 11, 2013 Location: Near Heart of Texas Posts: 713 Once you complete this project, be sure to try the ballistic pendulum too!
 April 9, 2013, 10:18 AM #17 Idaho Spud Senior Member   Join Date: April 7, 2010 Posts: 324 I also thought this thread was going to be about the ballistics pendulum. Imagine my surprise. My technology is still 19th century, I guess. I always knew I was born too late. You can get guestimates as good simply by looking in the ballistics tables in the back of most reloading manuals. __________________ "I should have picked alcohol, drugs, or beating my wife..." Pete Rose Last edited by Idaho Spud; April 9, 2013 at 10:29 AM.
 April 9, 2013, 10:24 AM #18 Cesure Senior Member   Join Date: March 2, 2013 Posts: 131 I heard it was a PITA to calibrate a ballistic pendulum.
 April 9, 2013, 12:12 PM #19 BoogieMan Senior Member   Join Date: April 4, 2012 Location: South Jersey Posts: 1,912 If you shoot .45acp you can just pull the trigger, then watch your second hand until you hear the ping on the steel. __________________ Concentrated power is not rendered harmless by the good intentions of those who create it. Milton Freidman "If you find yourself in a fair fight,,, Your tactics suck"- Unknown
 April 9, 2013, 02:46 PM #20 Idaho Spud Senior Member   Join Date: April 7, 2010 Posts: 324 Good 'n', Boogie Man! __________________ "I should have picked alcohol, drugs, or beating my wife..." Pete Rose
April 9, 2013, 09:09 PM   #21
Unclenick
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Join Date: March 4, 2005
Location: Ohio
Posts: 12,125
Quote:
 Originally Posted by Idaho Spud My technology is still 19th century, I guess.
Try 18th century. 1742 to be exact. The 19th century saw the Bashforth and Boulangé electromechanical chronographs and some variations come into being.
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 April 9, 2013, 10:13 PM #22 Idaho Spud Senior Member   Join Date: April 7, 2010 Posts: 324 Wikipedia: Around 1800, the ballistic pendulum was used to measure the momentum of the projectile fired by a gun; dividing the momentum by the projectile mass gives the velocity. The 19th century was a hundred years long. __________________ "I should have picked alcohol, drugs, or beating my wife..." Pete Rose
 April 10, 2013, 09:58 AM #23 Unclenick Staff   Join Date: March 4, 2005 Location: Ohio Posts: 12,125 Idaho Spud, The ballistic pendulum was invented by Benjamin Robbins, who died in 1751. The main fact you have to keep in mind regarding the Wikipedia is you never know who's been editing it. "About 1800" is just plain sloppy on the editor's part. This Wikipedia entry has it right, though. Scroll down to the history. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member
April 10, 2013, 01:02 PM   #24
A pause for the COZ
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Location: Braham, Minnesota
Posts: 1,172
Quote:
 or end up getting shot
Who told on me?????

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